The invention relates generally to anesthetic vaporizers of the type in which a gas stream directed through the vaporizer is divided into two streams, namely, a first or carrier gas stream passed through a vaporizing chamber containing a volatile liquid anesthetic and a second or bypass stream to be combined with the first stream after it has become saturated with anesthetic for subsequent discharge from the vaporizer. The streams of gas are controlled by flow control valves, wherein one of such valves is automatically adjustable in response to the temperature of the first stream after it become saturated with anesthetic or the temperature existing within the vaporizing chamber.
In my prior U.S. Pat. Nos. 3,534,732 and 3,630,438, the flow control valve for the first or carrier gas stream is a composite control valve, wherein one valve part is formed of metal and a cooperating valve part is formed of plastic material having a relatively large positive linear coefficient of thermal expansion, that is, the material expands upon an increase in temperature, within the normal temperature range in which a vaporizer is normally used. The plastic material employed was preferably a fluorocarbon of which polytetrafluoroethylene, known as PTFE or TFE or more generally by the trademark Teflon, is an example. A significant problem with this material encountered in actual practice was its tendency to swell when exposed to various anesthetic materials with the result that stability problems were encountered in the calibration of the flow control valve in which it was employed This problem was minimized to some extent by presaturating the material with the anesthetic, under pressure, but calibration drift over time was experienced, due to variations in the saturation process or drying out of the material "on the shelf" prior to its being placed in service.